Functional and molecular characterization of NOS isoforms in rat neutrophil precursor cells

iNOS regulates hematopoietic stem and progenitor cells via mitochondrial signaling and is critical for bone marrow regeneration

Hematopoietic stem cells (HSCs) replenish blood cells under steady state and on demand, that exhibit therapeutic potential for Bone marrow failures and leukemia. Redox signaling plays key role in immune cells and hematopoiesis. However, the role of reactive nitrogen species in hematopoiesis remains unclear and requires further investigation. We investigated the significance of inducible nitric oxide synthase/nitric oxide (iNOS/NO) signaling in hematopoietic stem and progenitor cells (HSPCs) and hematopoiesis under steady-state and stress conditions. HSCs contain low levels of NO and iNOS under normal conditions, but these increase upon bone marrow stress. iNOS-deficient mice showed subtle changes in peripheral blood cells but significant alterations in HSPCs, including increased HSCs and multipotent progenitors. Surprisingly, iNOS-deficient mice displayed heightened susceptibility and delayed recovery of blood progeny following 5-Fluorouracil (5-FU) induced hematopoietic stress. Loss of quiescence and increased mitochondrial stress, indicated by elevated MitoSOX and MMPhi HSCs, were observed in iNOS-deficient mice. Furthermore, pharmacological approaches to mitigate mitochondrial stress rescued 5-FU-induced HSC death. Conversely, iNOS-NO signaling was required for demand-driven mitochondrial activity and proliferation during hematopoietic recovery, as iNOS-deficient mice and NO signaling inhibitors exhibit reduced mitochondrial activity. In conclusion, our study challenges the conventional view of iNOS-derived NO as a cytotoxic molecule and highlights its intriguing role in HSPCs. Together, our findings provide insights into the crucial role of the iNOS-NO-mitochondrial axis in regulating HSPCs and hematopoiesis.

Loss of Shp1 impairs myeloid cell function and causes lethal inflammation in zebrafish larvae

PTPN6 encodes SHP1, a protein tyrosine phosphatase with an essential role in immune cell function. SHP1 mutations are associated with neutrophilic dermatoses and emphysema in humans, which resembles the phenotype seen in motheaten mice that lack functional SHP1. To investigate the function of Shp1 in developing zebrafish embryos, we generated a ptpn6 knockout zebrafish line lacking functional Shp1. Shp1 knockout caused severe inflammation and lethality around 17 days post fertilization (dpf). During early development, the myeloid lineage was affected, resulting in a decrease in the number of neutrophils and a concomitant increase in the number of macrophages. The number of emerging hematopoietic stem and progenitor cells (HSPCs) was decreased, but due to hyperproliferation, the number of HSPCs was higher in ptpn6 mutants than in siblings at 5 dpf. Finally, the directional migration of neutrophils and macrophages was decreased in response to wounding, and fewer macrophages were recruited to the wound site. Yet, regeneration of the caudal fin fold was normal. We conclude that loss of Shp1 impaired neutrophil and macrophage function, and caused severe inflammation and lethality at the larval stage.

Neuronal Nitric Oxide Synthase (nNOS) in Neutrophils: An Insight

NO (nitric oxide) is an important regulator of neutrophil functions and has a key role in diverse pathophysiological conditions. NO production by nitric oxide synthases (NOS) is under tight control at transcriptional, translational, and post-translational levels including interactions with heterologous proteins owing to its potent chemical reactivity and high diffusibility; this limits toxicity to other cellular components and promotes signaling specificity. The protein-protein interactions govern the activity and spatial distribution of NOS isoform to regulatory proteins and to their intended targets. In comparison with the vast literature available for endothelial, macrophages, and neuronal cells, demonstrating neuronal NOS (nNOS) interaction with other proteins through the PDZ domain, neutrophil nNOS, however, remains unexplored. Neutrophil's key role in both physiological and pathological conditions necessitates the need for further studies in delineating the NOS mediated NO modulations in signaling pathways operational in them. nNOS has been linked to depression, schizophrenia, and Parkinson's disease, suggesting the importance of exploring nNOS/NO-mediated neutrophil physiology in relation to such neuronal disorders. The review thus presents the scenario of neutrophil nNOS from the genetics to the functional level, including protein-protein interactions governing its intracellular sequestration in diverse cell types, besides speculating possible regulation in neutrophils and also addressing their clinical implications.

Intestinal methicillin-resistant Staphylococcus aureus causes prosthetic infection via 'Trojan Horse' mechanism: Evidence from a rat model

Aims

Methicillin-resistant Staphylococcus aureus (MRSA) can cause wound infections via a 'Trojan Horse' mechanism, in which neutrophils engulf intestinal MRSA and travel to the wound, releasing MRSA after apoptosis. The possible role of intestinal MRSA in prosthetic joint infection (PJI) is unknown.

Methods

Rats underwent intestinal colonization with green fluorescent protein (GFP)-tagged MRSA by gavage and an intra-articular wire was then surgically implanted. After ten days, the presence of PJI was determined by bacterial cultures of the distal femur, joint capsule, and implant. We excluded several other possibilities for PJI development. Intraoperative contamination was excluded by culturing the specimen obtained from surgical site. Extracellular bacteraemia-associated PJI was excluded by comparing with the infection rate after intravenous injection of MRSA or MRSA-carrying neutrophils. To further support this theory, we tested the efficacy of prophylactic membrane-permeable and non-membrane-permeable antibiotics in this model.

Results

After undergoing knee surgery eight or 72 hours after colonization, five out of 20 rats (25.0%) and two out of 20 rats (10.0%) developed PJI, respectively. Strikingly, 11 out of 20 rats (55.0%) developed PJI after intravenous injection of MRSA-carrying neutrophils that were isolated from rats with intestinal MRSA colonization. None of the rats receiving intravenous injections of MRSA developed PJI. These results suggest that intestinal MRSA carried by neutrophils could cause PJI in our rat model. Ten out of 20 (50.0%) rats treated with non-membrane-permeable gentamicin developed PJI, whereas only one out of 20 (5.0%) rats treated with membrane-permeable linezolid developed PJI.

Conclusion

Neutrophils as carriers of intestinal MRSA may play an important role in PJI development.Cite this article: Bone Joint Res. 2020;9(4):152-161.

Enhanced immunosuppressive effects of 3,5-bis[4(diethoxymethyl)benzylidene]-1-methyl-piperidin-4-one, an α, β-unsaturated carbonyl-based compound as PLGA-b-PEG nanoparticles

Background: 3,5-Bis[4-(diethoxymethyl)benzylidene]-1-methyl-piperidin-4-one (BBP), a novel synthetic curcumin analogue has been revealed to possess strong in vitro and in vivo immunosuppressive effects. Purpose: The aim of present study was to prepare and characterize BBP-encapsulated polylactic-co-glycolic acid-block-polyethylene glycol (PLGA-b-PEG) nanoparticles and to evaluate its in vivo efficacy against innate and adaptive immune responses. Methods: Male BALB/c mice were orally administered with BBP alone and BBP- encapsulated nanoparticles equivalent to 5, 10 and 20 mg/kg of BBP in distilled water for a period of 14 days. The immunomodulatory potential was appraised by determining its effects on non-specific and specific immune parameters. Results: The results showed that BBP was successfully encapsulated in PLGA-b-PEG polymer with 154.3 nm size and high encapsulation efficiency (79%) while providing a sustained release for 48 hours. BBP nanoparticles showed significant enhanced dose-dependent reduction on the migration of neutrophils, Mac-1 expression, phagocytic activity, reactive oxygen species (ROS) production, serum levels of ceruloplasmin and lysozyme, immunoglobulins and myloperoxidase (MPO) plasma levels when compared to unencapsulated BBP. Enhanced dose-dependent inhibition was also observed on lymphocyte proliferation along with the downregulation of effector cells expression and release of cytokines, and reduction in rat paw oedema in BBP nanoparticles treated mice. At higher doses the suppressive effects of the BBP nanoparticles on various cellular and humoral parameters of immune responses were comparable to that of cyclosporine-A at 20 mg/kg. Conclusion: These findings suggest that the immunosuppressive effects of BBP were enhanced as PLGA-b-PEG nanoparticles.

A comparative study on immune-stimulatory and antioxidant activities of various types of ginseng extracts in murine and rodent models

Background

Ginseng (Panax ginseng) is a widely used traditional herbal supplement that possesses various health-enhancing efficacies. Various ginseng products are available in market, especially in the Korean peninsula, in the form of drinks, tablets, and capsules. The different ginseng types include the traditional red ginseng extract (RGE), white ginseng, and black red ginseng extract (BRGE). Their fermented and enzyme-treated products are also available. Different treatment regimens alter the bioavailability of certain compounds present in the respective ginseng extracts. Therefore, in this study, we aimed to compare the antioxidant and immune-stimulating activities of RGE, BRGE, and fermented red ginseng extract (FRGE).

Methods

We used an acetaminophen-induced oxidative stress model for investigating the reduction of oxidative stress by RGE, BRGE, and FRGE in Sprague Dawley rats. A cyclophosphamide-induced immunosuppression model was used to evaluate the immune-stimulating activities of these ginseng extracts in BALB/c mice.

Results

Our results showed that most prominently, RGE (in almost all experiments) exhibited excellent antioxidant effects via increasing superoxide dismutase, catalase, and glutathione peroxidase activities in the liver and decreasing serum 8-hydroxy-2′-deoxyguanosine, aspartate aminotransferase, and lactate dehydrogenase levels compared with the groups treated with FRGE and BRGE. Moreover, RGE significantly increased the number of white blood cells, especially T and B lymphocytes, and antibody-forming cells in the spleen and thymus, and it also activated a number of immune cell subtypes.

Conclusion

Taken together, these results indicate that RGE is the best supplement for consumption in everyday life for overall health-enhancing properties.

A Standardized Chemically Modified Curcuma longa Extract Modulates IRAK-MAPK Signaling in Inflammation and Potentiates Cytotoxicity

The TLR/IL-1R pathway is a critical signaling module that is misregulated in pathologies like inflammation and cancer. Extracts from turmeric (Curcuma longa L.) enriched in curcumin and carbonyls like turmerones have been shown to exert potent anti-inflammatory effects. The present study evaluated the anti-inflammatory activity, cytotoxic effect and the underlying mechanism of a novel chemically modified, non-carbonyl compound enriched Curcuma longa L. (C. longa) extract (CMCE). CMCE (1 or 10 μg/mL; 14 h) significantly decreased LPS (50-100 ng/mL) induced TNF-α and IL-1β production in THP-1 cells, human, and mouse whole blood as measured by ELISA. LPS-induced IRAK1, MAPK activation, TLR4 expression, TLR4-MyD88 interaction, and IκBα degradation were significantly reduced in CMCE pre-treated THP-1 cells as assessed by Western blotting. CMCE (30, 100, and 300 mg/kg; 10 days p.o.) pre-treated and LPS (10 mg/kg) challenged Swiss mice exhibited attenuated plasma TNF-α, IL-1β, nitrite, aortic iNOS expression, and vascular dysfunction. In a PI permeability assay, cell lines derived from acute myeloid leukemia were most sensitive to the cytotoxic effects of CMCE. Analysis of Sub-G1 phase, Annexin V-PI positivity, loss of mitochondrial membrane potential, increased caspase-3, and PARP-1 activation confirmed CMCE induced apoptosis in HL-60 cells. IRAK inhibition also sensitized HL-60 cells to CMCE induced cytotoxicity. The present study defines the mechanism underlying the action of CMCE and suggests a therapeutic potential for its use in sepsis and leukemia.

Immunosuppressive effects of the standardized extract of Phyllanthus amarus on cellular immune responses in Wistar-Kyoto rats

Phyllanthus amarus (family: Euphorbiaceae) is of immense interest due to its wide spectrum of biological activities. In the present study, the standardized 80% ethanol extract of P. amarus was investigated for its modulatory activity on various cellular immune parameters, including chemotaxis of neutrophils, engulfment of Escherichia coli by neutrophils, and Mac-1 expression, in leukocytes isolated from treated/nontreated Wistar-Kyoto rats. The detailed cell-mediated activity of P. amarus was also investigated, including analysis of the effects on T- and B-cell proliferation and CD4(+) and CD8(+) T-cell subsets in splenic mononuclear cells, and estimation of serum cytokine production by activated T-cells. The main components of the extract, phyllanthin, hypophyllanthin, corilagin, geraniin, ellagic acid, and gallic acid were identified and quantitatively analyzed in the extracts, using validated reversed-phase high-performance liquid chromatography (HPLC) methods. N-formyl-methionyl-leucyl-phenylalanine (fMLP)-induced neutrophils isolated from rats administered with the extract of P. amarus, at doses ranging from 100 to 400 mg/kg for 14 days, revealed a significant dose-dependent reduction in neutrophil migration (P<0.05). Similar patterns of inhibition were also observed in phagocytic activity and in fMLP-induced changes in expression of β2 integrin polymorphonuclear neutrophils. The results in P. amarus-treated rats also demonstrated a dose-dependent inhibition of both lipopolysaccharide-stimulated B-cell proliferation and concanavalin A-stimulated T-cell proliferation as compared with sensitized control. At a dose of 400 mg/kg (P<0.01), there was a significant decrease in the (%) expression of CD4(+) and CD8(+) in splenocytes and in serum cytokines of T helper (Th1) (IL-2 and IFN-γ) and Th2 (IL-4). In conclusion, P. amarus showed effective immunosuppressive activities in cellular immune response, by various immune regulatory mechanisms, and may be useful for improvement of immune-related disorders.

Immunostimulatory effects of the standardized extract of Tinospora crispa on innate immune responses in Wistar Kyoto rats

Tinospora crispa (TC) has been used in folkloric medicine for the treatment of various diseases and has been reported for several pharmacological activities. However, the effects of TC extract on the immune system are largely unknown. Therefore, the present study was aimed to investigate the immunomodulatory effects of a standardized 80% ethanol extract of the stem of TC on innate immune responses. Male Wistar Kyoto rats were treated daily at 100 mg/kg, 200 mg/kg, and 400 mg/kg doses of the extract for 21 days by oral gavage. The immunomodulatory potential of TC was evaluated by determining its effect on chemotaxis and phagocytic activity of neutrophils isolated from the blood of rats. To further elucidate the mechanism of action, its effects on the proliferation of T- and B-lymphocytes and T-lymphocytes subsets (CD4+ and CD8+) and on the secretion of Th1 and Th2 cytokines were also monitored. The main components of the extracts, syringin and magnoflorine, were identified and quantitatively analyzed in the extracts by using a validated reversed-phase high-performance liquid chromatography method. It was observed that the chemotactic activity of neutrophils obtained from extract-treated rats increased as compared to controls. A dose-dependent increase in the number of migrated cells and phagocytosis activity of neutrophils was observed. Dose-dependent increase was also observed in the T- and B-lymphocytes proliferation stimulated with concanavalin A (5 μg/mL) and lipopolysaccharide (10 μg/mL), and was statistically significant at 400 mg/kg (P>0.01). Apart from cell-mediated immune response, the concentrations of Th1 (TNF-α, IL-2, and IFN-γ) and Th2 (IL-4) cytokines were significantly increased in sera of rats treated with different doses as compared with the control group. From these findings, it can be concluded that TC possesses immunostimulatory activity and has therapeutic potential for the prevention of immune diseases.

Identification of free nitric oxide radicals in rat bone marrow: implications for progenitor cell mobilization in hypertension

Nitric oxide (NO) has been implicated in matrix metallopeptidase 9 (MMP9)-dependent mobilization of hematopoietic stem and progenitor cells from bone marrow (BM). However, direct measurement of NO in the BM remained elusive due to its low in situ concentration and short lifetime. Using NO spin trapping and electron paramagnetic resonance (EPR) spectroscopy we give the first experimental confirmation of free NO radicals in rodent BM. NO production was quantified and attributed to enzymatic activity of NO synthases (NOS). Although endothelial NOS (eNOS) accounts for most (66%) of basal NO, we identified a significant contribution (23%) from inducible NOS (iNOS). Basal NO levels closely correlate with MMP9 bioavailability in BM of both hypertensive and control rats. Our observations support the hypothesis that inadequate mobilization of BM-derived stem and progenitor cells in hypertension results from impaired NOS/NO/MMP9 signalling in BM, a condition that may be corrected with pharmacological intervention.

Suppression of dendritic cell maturation and T cell proliferation by synovial fluid myeloid cells from mice with autoimmune arthritis

OBJECTIVE

To determine whether myeloid cells (such as granulocytes) present in the synovial fluid (SF) of arthritic joints have an impact on adaptive immunity. Specifically, we investigated the effects of SF cells harvested from the joints of mice with proteoglycan-induced arthritis (PGIA), on dendritic cell (DC) maturation and antigen-specific T cell proliferation.

METHODS

We monitored DC maturation (MHCII and CD86 expression) by flow cytometry upon coculture of DCs with SF cells or spleen myeloid cells from mice with PGIA. The effects of these myeloid cells on T cell proliferation were studied using T cells purified from PG-specific T cell receptor (TCR)-transgenic (Tg) mice. Phenotype analysis of myeloid cells was performed by immunostaining, reverse transcription-polymerase chain reaction, Western blotting, and biochemical assays.

RESULTS

Inflammatory SF cells significantly suppressed the maturation of DCs upon coculture. PG-TCR-Tg mouse T cells cultured with antigen-loaded DCs showed dramatic decreases in proliferation in the presence of SF cells. Spleen myeloid cells from arthritic mice did not have suppressive effects. SF cells were unable to suppress CD3/CD28-stimulated proliferation of the same T cells, suggesting a DC-dependent mechanism. SF cells exhibited all of the characteristics of myeloid-derived suppressor cells (MDSCs) and exerted suppression primarily through the production of nitric oxide and reactive oxygen species by granulocyte-like cells.

CONCLUSION

SF in the joints of mice with PGIA contains a population of granulocytic MDSCs that potently suppress DC maturation and T cell proliferation. These MDSCs have the potential to limit the expansion of autoreactive T cells, thus breaking the vicious cycle of autoimmunity and inflammation.

Identification of mannose receptor as receptor for hepatocyte growth factor β-chain: novel ligand-receptor pathway for enhancing macrophage phagocytosis

Hepatocyte growth factor (HGF), a heterodimer composed of the α-chain and β-chain, exerts multifunctional actions for tissue repair and homeostasis via its receptor, MET. HGF is cleaved by proteases secreted from inflammatory cells, and NK4 and β-chain remnant (HGF-β) are generated. Here, we provide evidence that HGF-β binds to a new receptor other than MET for promoting a host cell clearance system. By an affinity cross-linking, radiolabeled HGF-β was bound to liver non-parenchymal cells, particularly to Kupffer cells and sinusoidal endothelial cells, but not to parenchymal hepatocytes. The cross-linked complex was immunoprecipitated by anti-HGF antibody, but not anti-MET antibody, implying that HGF-β binds to non-parenchymal cells at a site distinct from MET. Mass spectrometric detection of the ligand receptor complex revealed that the binding site of HGF-β was the mannose receptor (MR). Actually, an ectopic expression of MR in COS-7 cells, which express no endogenous MR or MET, enabled HGF-β to bind these cells at a K(D) of 89 nM, demonstrating that MR is the new receptor for HGF-β. Interaction of HGF-β and MR was diminished by EGTA, and by an enzymatic digestion of HGF-β sugar chains, suggesting that MR may recognize the glycosylation site(s) of HGF-β in a Ca(2+)-dependent fashion. Notably, HGF-β, but not other MR ligands, enhanced the ingestion of latex beads, or of apoptotic neutrophils, by Kupffer cells, possibly via an F-actin-dependent pathway. Thus, the HGF-β·MR complex may provide a new pathway for the enhancement of cell clearance systems, which is associated with resolution of inflammation.

Activation of MDL-1 (CLEC5A) on immature myeloid cells triggers lethal shock in mice

Systemic inflammatory response syndrome (SIRS) is a potentially lethal condition, as it can progress to shock, multi-organ failure, and death. It can be triggered by infection, tissue damage, or hemorrhage. The role of tissue injury in the progression from SIRS to shock is incompletely understood. Here, we show that treatment of mice with concanavalin A (ConA) to induce liver injury triggered a G-CSF-dependent hepatic infiltration of CD11b+Gr-1+Ly6G+Ly6C+ immature myeloid cells that expressed the orphan receptor myeloid DAP12-associated lectin-1 (MDL-1; also known as CLEC5A). Activation of MDL-1 using dengue virus or an agonist MDL-1-specific antibody in the ConA-treated mice resulted in shock. The MDL-1+ cells were pathogenic, and in vivo depletion of MDL-1+ cells provided protection. Triggering MDL-1 on these cells induced production of NO and TNF-α, which were found to be elevated in the serum of treated mice and required for MDL-1-induced shock. Surprisingly, MDL-1-induced NO and TNF-α production required eNOS but not iNOS. Activation of DAP12, DAP10, Syk, PI3K, and Akt was critical for MDL-1-induced shock. In addition, Akt physically interacted with and activated eNOS. Therefore, triggering of MDL-1 on immature myeloid cells and production of NO and TNF-α may play a critical role in the pathogenesis of shock. Targeting the MDL-1/Syk/PI3K/Akt/eNOS pathway represents a potential new therapeutic strategy to prevent the progression of SIRS to shock.